1-Crotonyl-2,2,6-trimethylcyclohexanes

ABSTRACT

1-CROTONOYL-2,2,6-TRIMETHYLCYCLOHEXANE OCCURS IN FOUR STEREOISOMERIC FORMS. In particular the trans, E isomer has interesting organoleptic properties and is useful in the preparation of perfume and flavoring compositions. Processes for preparing the stereoisomers, in a pure form or as mixtures, are described.

The present invention relates to the four stereoisomers of1-crotonoyl-2,2,6-trimethylcyclohexane, more particularly to the trans,E isomer, which possesses unexpected interesting organoleptic propertiesand which therefore is useful in the preparation of a great variety ofperfume and flavouring compositions.

Although many examples of crotonoyl-trimethylcyclohexenes andcyclohexadienes are known as flavouring and perfume materials in therecent patent literature (as are the methods of their preparation),(e.g. Dutch Pat. app. No. 70,06649; Dutch Pat. app. No. 68,15985;British Pat. No. 1,240,309; Swiss Pat. No. 509,399; Swiss Pat. No.521,099; Swiss Pat. No. 521,298; E. Demole et al., Helv. Chim. Acta 53,541 (1970), surprisingly enough there is no mention in the prior art ofanalogous compounds with a saturated ring system. Careful testing of thefour stereoisomers has shown them to be not only totally different fromthe compounds with an unsaturated ring system but also strikinglydifferent from each other. This is less surprising than it may seem atfirst glance; it is known to anybody skilled in the art that the effecton the olfactive properties, as a consequence of hydrogenation of adouble bond or differences in the stereochemistry of a molecule, cannotbe predicted.

The trans, E isomer is fresh fruity and devoid of any woody and β-iononecharacter, which as a rule is observed in the afore-mentioned compoundswith an unsaturated ring system. Moreover the trans, E isomer has beenfound to be superior to both the latter compounds and to itsstereoisomers in all flavour and perfume applications tested.

The four possible stereoisomers of the compound of this invention,represented by formulas I - IV, can be prepared in a pure form or asmixtures by known per se methods.

An example of the preparation of III is the hydrogenation ofcis-1-acetyl-2,2,6-trimethyl-4-cyclohexene (V). The resultingcis-1-acetyl-2,2,6-trimethylcyclohexane (VI) is condensed withacetaldehyde and the obtained aldol product VII is dehydrated to III.This synthesis can be illustrated by reaction scheme A. Thehydrogenation of V can be performed in alcoholic solution with 10%palladium on charcoal as a catalyst. The resulting saturated ketone VIis then condensed with acetaldehyde under influence ofN-methylanilinomagnesium bromide as described by A. T. Nielsen et al inJ. Am. Chem. Soc. 73, 4696 (1951). The aldol product VII is subsequentlydehydrated in, for example, boiling methylene chloride or(azeotropically) in boiling benzene, both under the influence ofp-toluenesulphonic acid to cis,E-1-crotonoyl-2,2,6-trimethyl-cyclohexane (III).

An example of the preparation of I is the epimerization ofcis-1-acetyl-2,2,6-trimethylcyclohexane (VI) to the trans isomer VIII,which is condensed with acetaldehyde to the aldol product IX, and thendehydrated to I. This synthesis can be illustrated by reaction scheme B.Cis-1-Acetyl-2,2,6-trimethylcyclohexane (VI) can be epimerized bypolyphosphoric acid at elevated temperatures. The condensation step andthe dehydration are performed in the same way as described for the cisisomer III.

The starting material cis-1-acetyl-2,2,6-trimethyl-4-cyclohexene (V) canbe prepared by the method described by K. S. Ayyar et al in Chem. Comm.1973, 161 from 1,3-pentadiene and mesityl oxide in a Diels Alder-typereaction catalyzed by aluminum chloride.

An example of the preparation of a 70 : 30 mixture of I + II is theepoxidation of trans-dihydroionone (X), after which the resultingepoxide (XI) is converted by a Wharton reaction into a mixture of theunsaturated alcohols (XII and XIII), which are oxidized to a mixture ofthe corresponding ketones I + II. This synthesis can be illustrated byreaction scheme C. Trans-Dihydroionone (X) is epoxidized at 40°C with analkaline solution of 30% hydrogen peroxide. The obtained epoxide (XI) isrearranged by the addition of hydrazine hydrate and acetic acid inmethanolic solution at room temperature. The subsequent-oxidation of theformed mixture of unsaturated alcohols XII and XIII, yielding trans,E-1-crotonoyl-2,2,6-trimethylcyclohexane (I, 70%) and trans,Z-1-crotonoyl-2,2,6-trimethylcyclohexane (II, 30%) can be performed inseveral ways. A satisfactory method is the oxidation with manganesedioxide in an inert solvent such as pentane. On standing II isomerizesto I. The starting material trans-dihydroionone (X) can be prepared byknown methods, such as the condensation of dihydrocyclocitral withacetone under basic conditions (V. Prelog and H. Frick, Helv. Chim. Acta31, 417 (1948); M. de Botton, Bull. Soc. Chim. France 1966, 2212, 2466).

A further example of the preparation of a mixture of all fourstereoisomers is the epoxidation of α-ionone, after which the resultingepoxide XIV is hydrogenated to a mixture of dihydroionone epoxides XVand XI. These are converted by a Wharton-reaction into a mixture of theunsaturated alcohols XII, XIII, XVI and XVII, which are oxidized to amixture of the corresponding ketones. This synthesis can be illustratedby reaction scheme D. α-Ionone is epoxidized at 40°C with an alkalinesolution of 30% hydrogen peroxide. The obtained epoxide XIV ishydrogenated in acetic acid solution with platinum as the catalyst tothe dihydroionone epoxides XV and XI, which are rearranged by additionof hydrazine hydrate and acetic acid in methanolic solution at roomtemperature. The subsequent oxidation of the formed mixture of theunsaturated alcohols XII, XIII, XVI and XVII, yielding a mixture of thefour possible stereoisomers I, II, III, and IV respectively, of1-crotonoyl-2,2,6-trimethylcyclohexane, can be performed in severalways. A satisfactory method is the oxidation with manganese dioxide inan inert solvent as for example pentane. The Z isomers II and IV haveeach been isolated in pure form by preparative vapour phasechromatography.

The trans, E-1-crotonoyl-2,2,6-trimethylcyclohexane possesses a powerfulodour that can be described as very natural fruity, rich and warm, withan earthy-minty shading that accentuates the natural character. Itstenacity, when smelled on evaporation-blotterstrips, is very good andmakes this compound of great interest for use in compositions of floraland/or woody character like iris, mimosa, boronia, tobacco, and fancybouquets.

Use levels in floral compositions may vary within a wide range,preferably between 0.05% and 5%, whereas in compositions with a tobaccoleaf or a rose leaf character the level may be considerably higher. Inflavour compositions, use levels may vary within a wide range as well;in either case the powerful flavour of trans,E-1-crotonoyl-2,2,6-trimethylcyclohexane is obvious. In flavouringcompositions the percentage of trans,E-1-crotonoyl-2,2,6-trimethylcyclohexane can be varied between 0.001%and 1% of the flavouring composition, depending on the choice of theother ingredients. Moreover, trans,E-1-crotonoyl-2,2,6-trimethylcyclohexane is very effective in improvingthe flavour of natural extracts such as raspberry concentrates and otherberry or stone fruit concentrates. As little as 0.004% of trans,E-1-crotonoyl-2,2,6-trimethylcyclohexane in a natural raspberryconcentrate dramatically improves the raspberry flavour. This levelcorresponds with 0.1 ppm of trans,E-1-crotonoyl-2,2,6-trimethylcyclohexane in the finished product. Thelevel of trans, E-1-crotonoyl-2,2,6-trimethylcyclohexane in finishedproducts like beverages, icecream, candy, dessert mixes etc. is thususually below 1 ppm and sometimes as low as 0.1 ppb. This may be higherfor chewing gum.

The organoleptic quality of cis,E-1-crotonoyl-2,2,6,-trimethylcyclohexane is quite different from thatof the trans, E-isomer. The effect is far less fruity, while theearthy-minty aspect becomes dominating. The cis, E isomer is of littlevalue for use in flavouring compositions. The two Z isomers were foundto be of far less interest for either perfume or flavouring purposes.

EXAMPLE 1 Preparation of cis-1-acetyl-2,2,6-trimethylcyclohexane (VI)

464 g 1-acetyl-2,2,6-trimethyl-4-cyclohexene (V, prepared according toK. S. Ayyar Chem. Comm. 1973, 161) (2.8 moles) in 800 ml of ethanol and3 g 10% palladium on charcoal are hydrogenated in an autoclave under apressure of 50 atm and at 50°C. After the uptake ceases, the reactionmixture is filtered and concentrated by distillation under reducedpressure. The product cis-1-acetyl-2,2,6-trimethylcyclohexane (VI,containing about 10% of the trans isomer) is collected at 83°-88°C/12mm; yield 420 g (90%).

EXAMPLE 2 Preparation ofcis-1-(2,2,6-trimethylcyclohexyl)-3-butanol-one-1 (VII)

To 750 ml of an etheral solution of ethylmagnesium bromide (preparedfrom 302 g (2.7 moles) of ethyl bromide and 58,7 g (2.4 moles) magnesiumturnings in 550 ml of ether) is added with cooling and stirring asolution of 238 g (2.2 moles) of freshly distilled dry N-methylanilinein 700 ml of dry benzene (N₂ atmosphere). To the above freshly preparedsolution of N-methylanilinomagnesium bromide is added during 25- 30minutes a solution of 370 g (2.2 moles) of 1-acetyl-2,2,6-trimethylcyclohexane (VI) in 370 ml of dry benzene while keeping the temperatureat 15°C. After the addition of the ketone, the solution is allowed tostand for 30 minutes. A solution of 145.5 g (3.3 moles) of freshlydistilled acetaldehyde in 150 ml of dry benzene is then added during 45minutes, keeping the temperature at -13° to -10°C. After the addition ofthe aldehyde, the solution is allowed to stand for 90 minutes at thesame temperature. 2000 ml of 3N hydrochloric acid is then added withstirring and cooling. The organic layer is separated and washed 6 timeswith 1000 ml 3N hydrochloric acid (to remove the N-methylaniline) andfinally with 500 ml of water, 500 ml of sodium bicarbonate solution, andthen water. The combined organic layers are dried over, anhydrous sodiumsulfate and the solvents are removed by distillation at reducedpressure. The residue is distilled through a short Vigreux column. Theproduct, cis-1-(2,2,6-trimethylcyclohexyl)-3-butanolone-1 (containingabout 10% of the trans isomer) is collected at 98°-104°C/1 mm; yield 320g (70%).

EXAMPLE 3 Preparation of cis, E-1-crotonoyl-2,2,6-trimethylcyclohexane(III)

A solution of 320 g (1.5 moles) of the ketol prepared in Example 2 in1000 ml of benzene containing 2 g p-toluenesulphonic acid is heated inan apparatus for azeotropical water separation (Dean-Stark) till no morewater separates. The reaction mixture is washed with a solution ofsodium bicarbonate till neutral reaction and dried over anhydrous sodiumsulfate. The solvent is removed by distillation at reduced pressure andthe residue is distilled through a short Vigreux column. The product,cis, E-1-crotonoyl-2,2,6-trimethyl-cyclohexane (III, contains about 10%of the trans isomer) is collected at 76°C/1 mm; yield 273 g (94%).Recrystallization from pentane gives cis,E-1-crotonoyl-2,2,6-trimethylcyclohexane in high purity (m.p. 27°-28°C).

EXAMPLE 4 Conversion of a mixture of predominantlycis-1-acetyl-2,2,6-trimethyl cyclohexane (VI) into a mixture ofpredominantly the trans isomer (VIII)

A mixture of 185 g mostly cis-1-acetyl-2,2,6-trimethylcyclohexane (asprepared in example 1) and 550 g of polyphosphoric acid is heated at150°C for about one hour. The reaction mixture is cooled to below 100°C,whereafter crushed ice is added. The mixture is extracted with benzene.The obtained extract is washed subsequently with water, a solution ofsodium bicarbonate and again water, and dried over anhydrous sodiumsulfate. The solvent is removed by distillation at reduced pressure andthe residue is distilled through a short Vigreux column. The product,predominantly trans-1-acetyl-2,2,6-trimethylcyclohexane, is collected at85°-88°C/10 mm; yield 155 g (84%).

EXAMPLE 5 Preparation of trans,1-(2,2,6-trimethylcyclohexyl)-3-butanolone-1 (IX)

By repeating of the procedure described in example 2 but replacingcis-1-acetyl-2,2,6-trimethylcyclohexane (VI) by the trans isomer VIII(as prepared in example 4) there is obtained 67% of a mixture of theketols IX and VII, b.p. 105°-110°C/1 mm.

EXAMPLE 6 Preparation of trans, E-1-crotonoyl-2,2,6-trimethylcyclohexane(I)

By repeating the procedure described in Example 3 but now starting from130 g (0.61 mole) of the ketol mixture prepared in Example 5, there isobtained 99 g (84%) of a 87:13 mixture of trans, E (I) and cis,E-1-crotonoyl-2,2,6-trimethyl-cyclohexane (III), b.p. 92°-94°C/12 mm.Recrystallization from pentane gives trans,E-1-crotonoyl-2,2,6-trimethyl-cyclohexane in high purity, m.p. 8° - 9°C.

EXAMPLE 7 EPOXIDATION OF TRANS-DIHYDROIONONE (X)

130 ml of a 30% aqueous hydrogen peroxide solution (1.1.moles) aredropped with stirring into a solution of 97 g (0.5 mole)trans-dihydroionone and 40 ml 4N sodium hydroxide solution in 500 ml ofmethanol. The reaction mixture is kept at 40°C during 14 hours and thendiluted with 2.5 liters of water, saturated with sodium chloride andextracted three times with 200 ml of methylene chloride. The combinedorganic layers are washed with water and dried over anhydrous sodiumsulfate.

The solvent is removed by distillation at atmospheric pressure and theresidue is distilled through a short Vigreux column. The product,trans-dihydroionone epoxide is collected at 90°-92°C/1 mm; yield 82 g(80%).

EXAMPLE 8 Preparation of trans, E and trans,Z-1-(2,2,6-trimethylcyclohexyl)-2-butenol-2 (XII and XIII)

In a 1-L three-necked flask fitted with a mechanical stirrer, athermometer and a nitrogen inlet tube is placed a solution of 75 g (0.36moles) trans-dihydroionone epoxide (XI) in 360 ml of dry methanol. Drynitrogen is let in and within 10 minutes 53,5 g (1.0 mole) 99% hydrazinehydrate is added at a temperature of about 15°C while cooling with icewater.

Acetic acid (4.3 ml) is then added and nitrogen is evolved. Thetemperature is kept around 15°C for 4 hours after which the nitrogenevolution subsides. The reaction mixture is diluted with 1 liter ofwater, then saturated with sodium chloride and extracted with ether. Thecombined organic layers are subsequently washed with water, a solutionof sodium bicarbonate till neutral reaction, and again with water. Theetheral solution is dried over anhydrous sodium sulfate and the solventremoved by distillation at atmospheric pressure. The residue isdistilled through a short Vigreux column. The product, a mixture oftrans, E and trans, Z-1-(2,2,6-trimethyl-cyclohexyl)-2-butenol-1 (XIIand XIII) is collected at 80°-86°C/0,3 mm; yield 38 g (55%).

EXAMPLE 9 Oxidation of trans, E and trans,Z-1-(2,2,6-trimethylcyclohexyl)-2-butenol-1 (XII and XIII)

A solution of 7 g of the mixture of alcohols (obtained as described inExample 8), in 350 ml of dry pentane is stirred with 70 g of activatedmanganese dioxide during 35 hours. The course of the reaction isfollowed by gas chromatographic analysis. The inorganic material isremoved by filtration and the solvent by distillation at atmosphericpressure. The product, 1-crotonoyl-2,2,6-trimethylcyclohexane iscollected by distillation at 74°C/1 mm; yield 3.5 g (50%). The twocomponents were separated by preparative vapour phase chromatography andfound (from their IR and NMR spectra) to be the trans, Z (II) and trans,E (I) forms (30:70). On standing II isomerizes to I.

EXAMPLE 10 Epoxidation of α-ionone

A solution of 150 g (0.78 mole) of α-ionone and 80 ml of 6N sodiumhydroxide solution in 865 ml of methanol is brought to 35°C. 282 ml of a35% aqueous hydrogen peroxide solution (2.9 moles) are added withstirring during 45 minutes. The reaction mixture is kept at 35°-40°Cduring 4 hours and then concentrated to 500 ml. The residue is dilutedwith 300 ml of water, saturated with sodium chloride and extracted threetimes with 200 ml of chloroform. The combined organic layers are washedwith water and dried over anhydrous sodium sulfate. The solvent isremoved by distillation at reduced pressure and the residue is distilledthrough a short Vigreux column. The product, α-ionone epoxide (XIV), iscollected at 98°-102°C/1 mm; yield 114 g (70%).

EXAMPLE 11 Hydrogenation of α-ionone epoxide (XIV)

A solution of 130 g α-ionone epoxide (XIV) (0.62 mole) in 300 ml ofglacial acetic acid is hydrogenated in a Parr hydrogenation apparatuswith 1 g platinum oxide as a catalyst under a pressure of 50 p.s.i. tillthe uptake ceases. The small amount of dihydroionol epoxide which isalso formed, is reoxidized by adding enough chromic acid solution inwater at 25°-35°C to create a persistent orange-red colour for one hour.The reaction mixture is diluted with 1 liter of water, then extractedthree times with pentane. The combined organic layers are washed withwater and a solution of sodium bicarbonate till neutral reaction anddried over anhydrous sodium sulfate. The solvent is removed bydistillation at reduced pressure and the residue is distilled through ashort Vigreux column. The product, consisting of cis (90%) (XV) andtrans (10%) (XI) dihydroionone epoxide is collected at 96°-97°C/1 mm;yield 95 g (70%).

EXAMPLE 12 Preparation of 1-(2,2,6-trimethylcyclohexyl)-2-butenol-1

The same procedure as is described in Example 8 is applied to 90 g (0,42mole) of the mixture of cis- and trans- dihydroionone epoxide, asobtained in Example 11. The product, a mixture of all four stereoisomersof 1-(2,2,6-trimethylcyclohexyl)-2-butenol-1 is collected at 92°-96°C/1mm; yield 33 g (40%).

EXAMPLE 13 Oxidation of the mixture of alcohols from example 12

The same procedure as is described in Example 9 is applied to 25 g (0,13mole) of the mixture of alcohols obtained in Example 12. The product, amixture of all four stereoisomers of1-crotonoyl-2,2,6-trimethylcyclohexane (III:IV:I:II in a ratio of60:27:9:4) is collected by distillation at 80°-90°C/1 mm; yield 13 g(50%). cis, Z (IV) is isolated from the foregoing mixture by preparativevapour phase chromatography.

EXAMPLE 14

Preparation of a raspberry flavouring composition. A raspberryflavouring composition was prepared by mixing together the followingingredients (parts by weight):

    α-terpineol          10                                                 p-hydroxyfenylbutanone     5                                                  Isoamyl acetate            10                                                 Isobutyl acetate           6                                                  α-Ionone             10                                                 Buchu oil 10% in propylene glycol                                                                        2                                                  Dimethylsulfide 10% in propylene glycol                                                                  2                                                  Benzyl alcohol             25                                                 Propylene glycol           926                                                                           total  996                                     

Various test compositions were prepared as follows:

a. A 10% propylene glycol solution, oftrans,E-1-crotonoyl-2,2,6-trimethylcyclohexane (4 g) was added to 996 gof above-mentioned composition.

b. A 10% propyleneglycol solution ofcis,E-1-crotonoyl-2,2,6-trimethylcyclohexane (4 g) was added to 996 g ofthe above-mentioned composition.

c. A 10% propylene glycol solution of E-β-damascenone (E. Demole et al.,loc. cit.) (4 g) was added to 996 g of the above-mentioned composition.

d. A 10% propylene glycol solution of E-β-damascone (E. Demole et al.,loc. cit.) (4 g) was added to 996 g of the above mentioned composition.

A `control` composition was prepared by adding 4 g of additionalpropylene glycol to 996 g of the above mixture.

The flavour effect of the control and test compositions thus obtainedwas compared by application in drinks prepared by adding 15 ml ofconcentrated sugar syrup (60%), 0.1 g of citric acid 50% in water, 85 mlwater and 1 g of a 1% solution of the control and test composition.

Comparative tests by a test panel gave the following results.

The drink with the `control` flavour composition possesses certainraspberry flavour characteristics, but not very pronounced or `natural`.

The drink with flavour (a) was found to be tastewise a definiteimprovement over the control. A natural raspberry effect is the result.This shows that addition of a certain quantitiy (as indicated) oftrans,E-1-crotonoyl-2,2,6-trimethylcyclohexane is a very desirableimprovement.

The drink with flavour (b) still has a thin taste; no improvement overthe control.

The drink with flavour (c) was found to be some improvement over the`control` drink but the taste effect of E-β-damascenone is quite jammyand woody, which effect is less natural and desirable when compared withflavour (a).

The drink with flavour (d) was also found to possess a rather jammy andwoody (ionone-like) taste. This type of taste is much less desirablethan the taste of the drink with flavour (a).

EXAMPLE 15 Preparation of a rhubarb flavouring composition.

A rhubarb flavouring composition was prepared by mixing together thefollowing ingredients (parts by weight):

    Styrallyl acetate         40                                                  Dimethylbenzylcarbinyl butyrate                                                                         30                                                  Ethyl acetate             10                                                  Ethyl butyrate            5                                                   Lemon oil                 15                                                  Benzyl alcohol            50                                                  Propylene glycol          846                                                                           total  996                                      

A `control` composition was prepared by adding 4 g of additionalpropylene glycol to 996 g of the above mixture.

Test compositions were prepared as follows:

a. A 10% solution (in propylene glycol) oftrans,E-1-crotonoyl-2,2,6-trimethylcyclohexane (4 g) was added to 996 gof the basic composition.

b. A 10% solution (in propylene glycol) ofcis,E-1-crotonoyl-2,2,6-trimethylcyclohexane (4 g) was added to 996 g ofthe basic composition.

c. A 10% solution (in propylene glycol) of E-β-damascenone (E. Demole etal., loc. cit.) (4 g) was added to 996 g of the basic composition.

d. A 10% solution (in propylene glycol) of E-β-damascone (E. Demole etal., loc. cit.) added to 996 g of the above mentioned composition.

The flavour effect of the compositions thus obtained was compared byapplication in drinks prepared as mentioned in example 14. Comparativetests by a test panel gave the following results.

The drink with flavour (a) was found to possess a rhubarb-like tastewith an effect of increased ripeness and sweetness, when compared withthe taste of the `control` drink.

The drink with flavour (b) was found to be slightly metallic in taste,and no improvement over the control.

The drink with flavour (c) had lost the characteristics of rhubarb, whencompared with the control. The taste of the drink was found to be toosweet and woody to be characteristic rhubarb.

The same effect was found in the drink with flavour (d).

EXAMPLE 16 Flavouring of natural juices and concentrates.

A red currant juice concentrate was mixed with 1 ppm of the compoundsmentioned earlier, thus yielding the following products:

a. Red currant juice concentrate with 1 ppm oftrans,E-1-crotonoyl-2,2,6-trimethylcyclohexane.

b. The same concentrate with 1 ppm ofcis,E-1-crotonoyl-2,2,6-trimethylcyclohexane.

c. The same concentrate with 1 ppm of E-β-damascenone (E. Demole et al.,loc. cit.).

d. The same concentrate with 1 ppm E-β-damascone (E. Demole et al., loc.cit.).

The flavour of the concentrates a, b, c, d and a `control` was comparedby tasting drinks prepared by adding 15 ml of concentrated sugar syrup(60%), 0.1 g of citric acid 50% in water, 85 ml of water and 0.3 g ofthe juice concentrate. Comparative tests by a test panel gave thefollowing results.

Concentrate (a) was found to possess a strongly increased very naturalcurrant taste when compared with the `control` drink.

Concentrate (b) was found to possess a much less natural currant taste.

Concentrate (c) was found to have a jammy-raspberry-like character whichdoes not bring the product closer to natural red currant taste. The sameis true for concentrate (d) but here the effect of raspberry similarityis even less pronounced.

We claim:
 1. A 1-Crotonoyl-2,2,6-trimethylcyclohexane mixture comprisingthe following stereo isomers;trans,E-1-crotonoyl-2,2,6-trimethylcyclohexane,trans,Z-1-crotonoyl-2,2,6-trimethylcyclohexane,cis,E-1-crotonoyl-2,2,6-trimethylcyclohexane, andcis,Z-1-crotonoyl-2,2,6-trimethylcyclohexane. 2.Trans,E-1-crotonoyl-2,2,6-trimethylcyclohexane. 3.Cis,E-1-crotonoyl-2,2,6-trimethylcyclohexane.